Drug & supplement interaction

Lunasin + Letrozole

Letrozole brand name: Femara.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 13, 2026
The bottom line No known interaction

We found no known interaction between Lunasin and Letrozole in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

Lunasin and Letrozole

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Letrozole and Lunasin in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

Worth understanding: our licensed dataset holds no drug-interaction record for Lunasin at all — not against Letrozole, and not against any other medication we track. This verdict therefore rests on the absence of any recorded data, not on research that looked at this combination and found nothing. We cannot rule an interaction out.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Lunasin safety at a glance

Lunasin overall Not established Lunasin is found in common foods, but the safety of concentrated supplements has not been well studied.
Pregnancy Avoid There is not enough safety data, so concentrated supplements should be avoided during pregnancy.
Breastfeeding Avoid There is not enough safety data, so concentrated supplements should be avoided while breastfeeding.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Letrozole and Lunasin? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

No Interaction Found — But Data Suggests Lunasin and Letrozole May Share a Side Effect

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do.

  • Nausea Additional detail

    Lunasin

    “There is currently a limited amount of information on the adverse effects of lunasin. Orally, adverse effects reported in clinical research include nausea, constipation (including obstipation), diarrhea, early satiety, decreased appetite, bloating, abdominal pain, and flatulence.”

    Lunasin · Natural Medicines adverse-effect record, reported in constipation.

    2 sources cited
    1. 104526. Bedlack RS, Wicks P, Vaughan T, et al. Lunasin does not slow ALS progression: results of an open-label, single-center, hybrid-virtual 12-month trial. Amyotroph Lateral Scler Frontotemporal Degener. 2019 May;20(3-4):285-293. PubMed
    2. 104527. Haddad Tabrizi S, Haddad E, Rajaram S, Oda K, Kaur A, Sabaté J. The effect of soybean lunasin on cardiometabolic risk factors: A randomized clinical trial. Subst Use Misuse. 2019;54(9):1530-1540. PubMed

    “Orally, lunasin can cause nausea, constipation, diarrhea, early satiety, decreased appetite, bloating, abdominal pain, and flatulence. Two cases of obstipation requiring hospitalization have been reported following administration of lunasin.”

    Lunasin · Natural Medicines adverse-effect record, reported in constipation.

    2 sources cited
    1. 104526. Bedlack RS, Wicks P, Vaughan T, et al. Lunasin does not slow ALS progression: results of an open-label, single-center, hybrid-virtual 12-month trial. Amyotroph Lateral Scler Frontotemporal Degener. 2019 May;20(3-4):285-293. PubMed
    2. 104527. Haddad Tabrizi S, Haddad E, Rajaram S, Oda K, Kaur A, Sabaté J. The effect of soybean lunasin on cardiometabolic risk factors: A randomized clinical trial. Subst Use Misuse. 2019;54(9):1530-1540. PubMed

    Letrozole

    Listed in the ADVERSE REACTIONS section of the FDA label for Letrozole. Read the label on DailyMed ›

Reported for Lunasin but not commonly for Letrozole: reduced appetite, stomach pain, constipation and bloating or gas.

Effects for Letrozole come from the ADVERSE REACTIONS section of its FDA label; effects for Lunasin come from the Natural Medicines adverse-effect record, quoted above. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

From our Q&A

Questions About Lunasin or Letrozole

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Lunasin or Letrozole, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Letrozole

This page covers Lunasin only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Letrozole page lists 142 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), 7-methoxyflavone (moderate) and Acacia Rigidula (moderate).

By severity: 3 major · 99 moderate · 40 minor.

From our pharmacist’s overview on the Letrozole page

“Letrozole (Femara) is prescribed to keep hormone-driven breast cancer from returning, so a supplement that shifts its blood level can quietly undercut treatment. Give this list of 142 ingredients genuine respect, and learn the three major entries first.”

Reviewed by 2 · Jul 18, 2026

Open the Letrozole interaction page

How much people look this up

Where Lunasin and Letrozole Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Lunasin
Steady interest

#909 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Letrozole
Top 5%

#50 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Lunasin reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Lunasin and Letrozole records this page draws on were last updated July 10, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Supplement

About Lunasin

What is Lunasin?

  • Cholesterol and heart health
  • General immune support
  • Antioxidant support
  • Anti-inflammatory support
  • Cancer-prevention interest (unproven)

Lunasin is a small protein (peptide) found naturally in soybeans and some other seeds and grains. Laboratory and animal studies suggest it may have antioxidant, anti-inflammatory, and cholesterol-related effects, but solid human evidence is very limited. Talk with your pharmacist or doctor before using a lunasin supplement.

Seeds (most studied in soybean) · Capsules, powders, and protein extracts (often soy-derived)

An interaction check asks whether these two react with each other — it does not ask whether Lunasin is a good idea for someone in your situation. Here is what our Lunasin record says about it on its own.

Lunasin: dosing

There is no established standard dose for lunasin supplements. The amounts used in research vary, and product labels differ from brand to brand.If you choose to try a product, follow the directions on the label and do not exceed them. Because quality and purity of supplements can vary, look for brands that use independent third-party testing.

From our Lunasin monograph — the full record covers uses, side effects and every documented interaction.

Read the full Lunasin monograph & all interactions
Medication

About Letrozole

What Is Letrozole Used For?

Brand name: Femara

Letrozole (brand name Femara) is used to treat breast cancer in postmenopausal women whose tumors are driven by estrogen. It is used in three settings: as adjuvant (after-surgery) treatment for hormone receptor positive early breast cancer; as extended adjuvant treatment for women who have already completed about five years of tamoxifen therapy; and as first- or second-line treatment for locally advanced or metastatic (spread) breast cancer.

Femara is specifically indicated for first-line treatment of hormone receptor positive or receptor-unknown locally advanced or metastatic breast cancer, and for advanced breast cancer in women whose disease has progressed after antiestrogen therapy.

See full Letrozole drug information
Keep checking

Other Drugs & Lunasin

Browse every other medication we’ve checked against Lunasin — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
0Moderate
0Minor
2,829No known interaction
2,829 No interaction
No interaction 2,829 drugs checked — show the list

We also checked Lunasin against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,829 medications checked with no known interaction — see the full Lunasin list.

See the full Lunasin interactions page
See every supplement checked against Letrozole, ranked by severity
Evidence & sources

Lunasin References

The 2 references that drive our Lunasin monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Bedlack RS, Wicks P, Vaughan T, et al. Lunasin does not slow ALS progression: results of an open-label, single-center, hybrid-virtual 12-month trial. Amyotroph Lateral Scler Frontotemporal Degener. 2019 May;20(3-4):285-293. PubMed
  2. Haddad Tabrizi S, Haddad E, Rajaram S, Oda K, Kaur A, Sabaté J. The effect of soybean lunasin on cardiometabolic risk factors: A randomized clinical trial. Subst Use Misuse. 2019;54(9):1530-1540. PubMed

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Lunasin and Letrozole Together: Common Questions

Is it safe to take Lunasin with Letrozole?
We do not list a known interaction between Lunasin and Letrozole. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Do Lunasin and Letrozole have any of the same side effects?
Yes — our sources link each of them separately to one of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.
Does Letrozole interact with any supplements?
Yes. Letrozole has documented interactions with 142 supplements in our database — Lunasin is not one of them. The Letrozole interaction page linked on this page lists every one, ranked by severity.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Where next

Keep Exploring

Lunasin monograph Uses, safety profile, and every drug interaction in one place Letrozole drug information The full plain-English guide to this medication Letrozole supplement interactions Every supplement checked against Letrozole, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 2 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Lunasin?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.